To combat mastitis infections which can be transmitted from cow to cow by contact with teat cup inflations used on several cows during one milking, backflushing systems have been developed which flush out the milk hose and teat cup cluster with hot water or a disinfectant solution after each cow has completed milking. Backflush systems have become particularly common with automatic milking machine detachers (or take-offs)--devices which sense when the cow is milked out and automatically remove the teat cups from the cow. The backflush operation may be automatically initiated in response to the signal provided by the automatic take-off which indicates that milking has been completed.
While backflush systems have become common because of their contribution to the control of mastitis, their use can result in the loss of a cumulatively significant amount of milk. This loss occurs when the hose and cluster are flushed out because there is typically about an ounce of rest milk left in the milking claw and another ounce in the milk hose when the milking machine is removed from the cow by an automatic detacher. Automatic take-off equipment generally shuts off the milking vacuum to the cow before the teat cups are removed to minimize irritation of the teats as the cups are drawn away from the cow. The shut-off of the vacuum also prevents contamination of the teat cups by material which could be drawn into the cups if the milking vacuum were left on.
The amount of milk lost per milking by backflushing is a small percentage of the total amount of milk given by the cow, since an average cow may yield 25 pounds of milk at each milking. However, the loss can become significant in larger dairy operations. If two ounces of milk are lost per milking, twice a day, approximately 91 pounds of milk are lost per milking cow per year as a result of the backflushing of the milking equipment. In addition, the final or rest milk given by the cow is higher than average in fat content. For example, if an average holstein gives milk in the range of 3.5 to 4% fat, the rest milk will often be as high as 7 to 8% fat. Under present milk purchasing rules, the dairymen are paid a premium for each additional percentage point of fat content. The rest milk remaining in the claw and milk hose therefore has a greater than average value to the dairyman. If the cows are milked three times a day rather than two, an even greater percentage of the total milk production will be lost in the backflush operation since the amount of rest milk remains constant while the production per milking generally is less than when the cows are milked twice daily.